OPERATIONAL BEHAVIOUR OF AN OFFSHORE MULTIPURPOSE SUPPORT VESSEL IN THE EASTERN MEDITERRANEAN SEA

The objective of this work is to analyse the operational behaviour of an offshore multipurpose support vessel designed to operate in the Eastern Mediterranean Sea. First, the seakeeping analysis is performed in a regular wave condition for different heading angles estimating heave and pitch motions through the strip theory. After that, the effects of the vertical acceleration on the bow, occurrence of slamming or hydrodynamic impact of the hull on the surface of the water; wetted deck, occurrence or invasion of water on the deck of the vessel and propeller emersion, motion sickness and wave-induced additional resistance are analysed. The present analysis is extended in an irregular sea condition, and the estimated seakeeping criteria are compared to the acceptable levels. In defining the most suitable operational mode of the offshore support vessels, multi-criteria decision techniques and probabilistic approach are employed to perform an adequate evaluation of the seakeeping performance accounting for different hazardous events through the service life.

Seakeeping index as generalized indicator of ship seakeeping performance

Object and purpose of research. This paper discusses the possibility of a ship design process that would consider seakeeping performance to the greatest extent possible. The purpose of this study was to work out a numerical indicator, an index, reflecting all the seakeeping properties relevant for suitability of given ship to its intended operational conditions. Materials and methods. The study was based on the data about various operational parameters of the ship under investigation. These data were further synthesized so as to obtain the most comprehensive picture of ship seakeeping behaviour in different operational conditions. Main results. The study yielded the method and the algorithm for the “seakeeping index” as an average annual probability that seakeeping performance of given ship will be adequate to the conditions of given water area. The method sug-gested in this paper for a generalized comparison of seakeeping properties can handle whatever variety of target parameters and whatever seakeeping standards for any kind of ship intended to operate in given water area, and the result of this comparison is given in form of a single number that can be further used to improve seakeeping parameters of given ship, as well as to estimate possible time of its fully-featured operation in given conditions, including cost efficiency analysis. Conclusion. For more accurate comparison, it is recommended to analyse target parameters as functions of both ship speed and wave heading angle keeping in mind that the assumption introduced, i.e. that these curves as functions of wave heading angle are cosines, is not necessarily true. In other words, it is recommended to rely on more accurate data, experimental or analytical, so as to take into account the effect of apparent frequencies upon these curves.

A new mathematical hull-form with 10-shape parameters for evaluation of ship response in waves

This study presents a new mathematical hull-form that is expressed as an explicit function with 10 hull-form parameters, which is called the Matsui hull-form in this study. The proposed hull-form was developed by expanding the modified Wigley hull-form so that the following 10 hull-form parameters can be independently varied: main dimensions $$L$$ L , $$B$$ B , $$d$$ d , fineness coefficients $${C}_{b}$$ C b , $${C}_{\mathrm{m}}$$ C m , $${C}_{\mathrm{w}}$$ C w , second moment of waterplane area coefficient $${C}_{\mathrm{w}2}$$ C w 2 , longitudinal center of buoyancy LCB and floatation LCF, and a parameter $$\beta$$ β related to anterior–posterior asymmetry. The main purpose of this hull-form is that it is utilized for the following two objects: the first is the simple evaluation of the seakeeping performance and wave loads in the early ship designing stage without any detailed offset data, and the second is a systematical study on the influence of a ship’s dimensions on the ship response in waves. This paper presents the derivation of the Matsui hull-form and the applicability of the proposed hull-from was confirmed by comparing the ship response in waves with the actual ships. Moreover, a sensitivity analysis of the ship response in waves was conducted as an example of the application of the proposed hull-form.

An Experimental Analysis of Active Pitch Control for an Assault Amphibious Vehicle Considering Waterjet-Hydrofoil Interaction Effect

The present study aims to reduce the pitch motion of an assault amphibious vehicle system in seaways by waterjet impeller revolution rate control. A series of seakeeping tests were performed in a towing tank with a 1/4.5-scale model. This vehicle is manufactured as a box-shaped hull, and since an appendage that generates lift force is attached, the amount of change in pitch motion is large according to the forward speed. For pitch motion reduction, the impeller revolution rate and resultant pitch moment were controlled through a proportional-integral-derivative controller. Improvements in seakeeping performance were examined in both regular and irregular conditions by the model tests in terms of root mean square of pitch motion. The tuned controller decreased pitch motion by more than 60%.